Polymeric materials are generally considered useful as viscosification agents when dissolved in an appropriate solvent system. The major reason for this viscosity enhancement is due to the very large dimensions of the individual polymer chain as compared to the dimension of the single solvent molecules. Any increase in size of the polymer chain will produce a corresponding enhancement in the viscosity of the solution. This effect is maximized, when the polymer is dissolved in a "good" solvent. Therefore, in general, a hydrocarbon soluble polymer is useful for thickening hydrocarbon solvents, while a water soluble polymer is appropriate for increasing the viscosity of aqueous systems. With regard to aqueous systems, polyelectrolytes are very useful and the most commonly used materials; however, the solution properties of these materials begin to deteriorate as low molecular additives (i.e., acids, bases or salts) are dissolved in the solution. These additives screen the charges that are fixed along the chain backbone which results in a decrease in the dimensions of the polymer molecule. The viscosity diminishes as long as the chain continues to shrink.
The instant invention discloses that intramolecular polymeric complexes (i.e., polyampholytes), composed of cationic, anionic and neutral monomeric units, can be useful in viscosifying aqueous solution systems. The former two moieties need not be present in an equimolar amount. More importantly, these polymeric materials possess higher viscosity in acid, base or salt solutions than in the corresponding fresh water system. Even more interesting is that these polymeric materials show a corresponding viscosity enhancement as the concentration of the dissolved acid, base or salt is increased. These viscosity results are unexpected since the general tendency of homogeneously charged macromolecules in these types of aqueous solutions shows a marked decrease in thickening efficiency.
Typical water soluble monomers incorporated into the terpolymers that are envisioned in the present invention are listed as follows:
Anionic: 2-acrylamido-2-methylpropane sulfonic acid, sodium styrene sulfonate, (meth)acrylic acid, 2-sulfoethylmethacrylate, and the like. PA0 Cationic: methacrylamidopropyltrimethylammonium chloride, dimethyldiallylammonium chloride, diethyldiallylammonium chloride, 2-methacryloxy-2-ethyltrimethylammonium chloride, trimethylmethacryloxyethylammonium methosulfate, 2-acrylamido-2-methylpropyltrimethylammonium chloride, vinylbenzyltrimethylammonium chloride, and the like. PA0 Nonionic: (N,N-dimethyl)acrylamide, hydroxyethyl(meth)acrylate, alkyl substituted acrylamides,(meth)acrylates, N-vinyllactanes (e.g., n-vinyl-2-pyrrolidone), and the like. PA0 Anionic: 2-acrylamido-2-methylpropane sulfonic acid, sodium styrene sulfonate, (meth)acrylic acid, 2-sulfoethylmethacrylate, and the like. PA0 Cationic: methacrylamidopropyltrimethylammonium chloride, dimethyldiallylammonium chloride, diethyldiallylammonium chloride, 2-methacryloxy-2-ethyltrimethylammonium chloride, trimethylmethacryloxyethylammonium methosulfate, 2-acrylamido-2-methylpropyltrimethylammonium chloride, vinylbenzyltrimethylammonium chloride, and the like. PA0 Nonionic: (N,N-dimethyl)acrylamide, hydroxyethyl(meth)acrylate, alkyl substituted acrylamides,(meth)acrylates, N-vinyllactanes (e.g., n-vinyl-2-pyrrolidone), and the like.
These monomers possess the appropriate water solubility for polymerization to take place.
Salamone et al., of the University of Lowell (Massachusetts), have investigated ampholytic polymers. They have studied the solution properties of divinylic cationic-anionic monomer pairs and also cationic-anionic monomer pairs with a neutral comonomer. This latter group of materials contains styrene as the neutral comonomer (J. Polym. Sci. Al, 18, 2983 [1980], which can be incorporated into the ampholytic macromolecular structure through both solution or emulsion polymerization schemes. Apparently, other neutral vinylic monomers (i.e., acrylamide) were also polymerized (Gordon Research Conference - 1981); but as of the present time, reports of this work have not been published in the scientific literature. However, in all of Salamone's work, detailed descriptions of this synthesis is reported. In all instances, the polymerization of tha anionic-cationic monomeric species occurred via an "ion-pair comonomers that have no nonpolymerizable counterions present" (J. Polym. Sci. - Letters, 15, 487 [1977]). The physical and chemical properties of these ion-pair comonomers are quite different than the individual ions (J. Polym. Sci. - Letters, 15, 487 [1977]).
Excess dissociable charges are not present within these polymeric materials.